1. Field of the Invention
This invention relates to a compressible sheet material usable for gaskets and, more particularly, to a non-asbestos sheet material for high-temperature gasketing applications.
2. Description of the Prior Art
In general, sheet gasket materials comprise sheets of uniform thickness often made of fibers held together by a suitable bonding agent. Where a gasket is exposed to a high-temperature environment, such as that in which a cylinder head gasket for an internal combustion engine normally operates, the sheet material comprising the gasket must exhibit not only superior heat resistance and sealability properties but also must have sufficient compressibility, resiliency, creep resistance and tensile strength.
In the past, all sheet materials for high-temperature gaskets have contained asbestos fibers. Asbestos fibers offer several advantages; they impart to the sheet material the desired performance and mechanical properties and are both inexpensive and readily available. More recently, however, concern about the health hazards associated with exposure to asbestos fibers has lead to the development of some non-asbestos sheet gasket materials.
These non-asbestos sheet gasket materials usually comprise a fiber component including inorganic and/or organic fibrous materials, an inorganic filler component and an organic binder. Sheet materials of this general composition are disclosed, for example, in U.S. Pat. Nos. 4,529,663, 4,529,653, 4,387,178 and 4,317,575. Unfortunately, most or all of the presently known non-asbestos sheet materials have proven to be not entirely satisfactory for use as high-temperature gaskets in many applicatons. That is, one or more defects, such as poor temperature tolerance due to burn-out of organic materials at relaively low temperatures, low tensile strength, lack of resiliency and insufficient cohesive strength to permit fabrication, plague the prior art non-asbestos materials.
Accordingly, an important objective of this invention is to provide a non-asbestos sheet material which fulfills the performance and mechanical requirements demanded of high-temperature gaskets.
It is a further objective of this invention to provide a non-asbestos sheet material suitable for use as a high-temperature gasket comprising inexpensive and readily available components.
It is a still further object of this invention to provide a non-asbestos sheet material suitable for use as a high-temperature gasket which can be manufactured by ordinary paper-making processes.